1. Field of the Invention
This invention relates to circuit card assemblies populated with components. More specifically, the invention is a circuit card assembly to include a particle damper for fundamental mode vibration damping.
2. Description of the Related Art
Circuit boards or cards are prone to mechanical-type failures as connections to their surface-mounted components experience fatigue/cracks when exposed to damaging vibration environments. Generally, component connection failures are due to the response of the primary bending mode of the circuit card when it is exposed to external excitations. The primary bending mode occurs at the card's fundamental frequency.
Attenuation of the primary bending mode response can be achieved by either increasing the stiffness of the circuit card or by providing damping mechanisms. An increase in the board stiffness increases the frequency and consequently decreases the resultant fatigue-related damage. However, increasing board stiffness involves increasing board thickness and/or inclusion of a small beam “stiffener” connected across the board as an additional constraint.
Vibration damping mechanisms directly attenuate the amplitude of the response at a particular mode without changing its frequency. Damping mechanisms/methods typically integrate a viscoelastic material into the board itself. However, board modifications to incorporate a viscoelastic material are generally not suitable for a board that has already been designed and built. The same is true of constrained-layer damping. Additionally, viscoelastic damping mechanisms are not very effective for frequencies greater than 50 Hz, are difficult to target at a specific mode, are very temperature dependent, and take up a lot of space.